Limit length of backreference in Javascript regular expression

I have a rather complex regular expression that matches a few strings. As part of the requirement, I need to replace some of the matching text with a truncated version. Using a backreference I get the text, but how do I use "string".replace() to truncate it e.g. only the first 10 characters? As there may be multiple matches per string, I do not want to manually extract and trunc开发者_运维问答ate the text.

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In Javascript 1.3 it's possible to pass a function as the replacement argument:

s = s.replace(/someregularexpression/g, function(x){ return x.substr(0, 10); });

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